Conventional golf balls can be divided into two general types or groups: solid balls and wound balls. The difference in play characteristics resulting from these different types of constructions can be quite significant.
Solid balls with a two-piece construction are generally most popular with the average recreational golfer, because they provide a very durable ball for a reasonable price while also providing maximum distance. Two piece solid balls are typically made with a single solid core, usually made of a crosslinked rubber, which is encased by a hard cover material. The combination of the core and cover materials, which are very rigid, provide a hard feel for the ball when it is struck with a club and provide a ball that is virtually indestructible by golfers. This combination of materials helps impart a high initial velocity to the ball, which results in improved distance. In addition, this combination provides balls having a relatively low spin rate, which tends to provide greater driver distance.
At the present time, however, the wound, ball generally remains the preferred ball of more advanced players due to its spin and feel characteristics. Wound balls typically have either a solid rubber or fluid-filled center around which many yards of a tensioned elastic thread or yarn are wrapped to form a wound core. Typically, the tensioned elastic thread is made of synthetic polyisoprene or natural rubber. For example, U.S. Pat. Nos. 5,674,137; 5,716,293; 5,816,937; 5,816,940; 5,816,941; 5,816,942; 5,888,151; and 5,976,034 relate to multi-layer, wound golf balls containing rubber thread windings. The wound core is then typically covered with a durable cover material, such as a SURLYN® or a similar material, or a softer “performance” cover, such as balata or polyurethane.
Typically, a single strand of thread is employed in forming the wound core. This thread can be wrapped at variable tension as disclosed in U.S. Pat. No. 4,783,078. Some balls, however, have used two or more different threads of different dimensions to form the wound core. In this case, the innermost thread may be wound at a different tension and with a different pattern than the outermost thread. Furthermore, the outermost thread is generally wound in a more open pattern to form larger gaps between the thread, which helps ensure good amalgamation between the cover and the wound core.
The United States Golf Association (USGA) has instituted a rule that prohibits the competitive use in any USGA sanctioned event of a golf ball that can achieve greater than an initial velocity of 76.2 meters per second (m/s), or 250 ft/s, when tested in a standardized device operated by the USGA (referred to hereinafter as “the USGA test”). An allowed tolerance of 2 percent, however, permits manufacturers to produce golf balls that achieve an initial velocity of up to 77.7 m/s (255 ft/s).
Players generally seek a golf ball that delivers maximum distance off the tee, which requires a high initial velocity upon impact. Therefore, in an effort to meet the demands of the marketplace while providing conforming balls, manufacturers typically strive to produce golf balls with initial velocities no greater than that permitted by the USGA test. Manufacturers try to provide these balls with a range of different properties and characteristics, such as spin and compression, to enhance short iron shots, as well.
To meet the needs of golfers having varying levels of skill, golf ball manufacturers are also concerned with varying the compression of the ball, which is a measurement of the deformation of a golf ball under a load. A ball with a higher compression feels harder than a ball of lower compression. Wound golf balls generally have lower compression and spin characteristics that are preferred by better players. Whether wound or solid, all golf balls become generally more resilient (i.e., have higher initial velocities) as compression increases. Manufacturers of both wound and solid construction golf balls must balance the requirement of higher initial velocity from higher compression with the desire for a softer feel from lower compression.
Wound balls typically enable a skilled golfer to have more control over the ball's flight and final position using short-iron shots than many non-wound balls. Particularly with approach shots into the green, the typically higher spin rate of soft covered, wound balls enables many golfers to stop the ball very near its landing position. Soft covered wound balls with their lower compression, however, tend to exhibit a lower initial velocity than hard covered solid balls. This characteristic, in combination with a higher spin rate than solid balls, means wound balls generally display shorter distance than hard covered solid balls when struck with a driver. The advantages of wound constructions over solid ones, however, are more related to spin and controllability than distance.
A softer feel is the result of a lower compression, but feel is also affected by cover hardness and thickness. In wound constructions, a thinner cover will have a softer feel, so manufacturers often strive to produce balls with the thinnest possible covers. The packing density of the windings and the cover formulation process can affect the thickness of the cover, but other factors related to the cover will also affect this thickness.
It is known in the art to modify conventional solid balls by altering the typical single layer core and single cover layer construction to provide a multi-layer ball having such as a dual cover layer and/or a ball having a mantle layer disposed between the cover and the core. Like the solid cores, various cover layers and mantle layers are typically formed of polybutadiene that is chemically erosslinked with zinc diaerylate and/or similar crosslinking agents. The playing characteristics of multi-layer balls, for example compression, can be tailored by varying the properties of one or more of these mantle layers, also known as intermediate layers.
A number of patents are directed towards modifying the properties of layers used in forming conventional solid balls, multi-layer balls having two or more cover layers, dual core layers, such as those having a mantle layer disposed between the cover and center, and/or wound balls. For example, U.S. Pat. Nos. 5,674,137; 5,816,937; 5,816,942; and 5,885,172 are directed to multi-layer wound golf balls having multi-layer covers. For example, U.S. Pat. Nos. 3,147,324; 5,816,937; and 5,885,172 are directed to golf balls, or methods for making such, having a polyurethane outer cover. For example, U.S. Pat. Nos. 5,716,293 and 5,020,803 are directed to wound golf balls having a dual layer liquid core.
U.S. Pat. No. 5,020,803 to Gendreau et al. discloses a golf ball containing a liquid-filled center, surrounded by a heavy-walled sphere, around which a wound layer is disposed to form a wound core. The heavy-walled sphere is preferably rubber and is between 0.16 and 0.64 cm thick.
British Patent No. GB 2337706 A to Sumitomo Rubber Industries, Ltd. discloses a multilayer wound golf ball having a dual layer center, both layer being formed from the same materials. The diameter of both center layers are limited, as are the JIS-C hardnesses, and the cover is made from a thermoplastic material.
Polyurethane is the product of a reaction between a polyurethane prepolymer and a curing agent. The polyurethane prepolymer is a product formed by a reaction between a polyol and a diisocyanate. The curing agents used previously are typically diamines or glycols. A catalyst is often employed to promote the reaction between the curing agent and the polyurethane prepolymer.
Polyurethanes are typically divided into two categories: thermosets and thermoplastics. Thermoplastic polyurethanes are typically formed by the reaction of a diisocyanate, such as 4,4′-diphenylmethane diisocyanate (“MDI”) or 3,3′-dimethyl-4,4′-biphenylene diisocyanate (“TODI”), and a polyol cured with a diol, such as 1,4-butanediol. Thermoset polyurethanes are typically formed by the reaction of a diisocyanate, such as 2,4-toluene diisocyanate (“TDI”) or methylene-bis-(4-cyclohexyl isocyanate) (“HMDI”), and a polyol which is cured with a polyamine, a triol such as trimethylol propane, or a tetrafunctional glycol, such as N,N,N′,N′tetra-bis-(2-hydroxypropyl) ethylenediamine.
U.S. Pat. No. 4,123,061 teaches a golf ball made from a polyurethane prepolymer of polyether and a curing agent, such as a trifunctional polyol, a tetrafunetional polyol, or a diamine. U.S. Pat. No. 5,334,673 discloses the use of two categories of polyurethane available on the market, i.e., thermoset and thermoplastic polyurethanes, for forming golf ball covers and, in particular, thermoset polyurethane covered golf balls made from a composition of polyurethane prepolymer and a slow-reacting amine curing agent and/or a difunctional glycol.
Unlike SURLYN® ionomer covered golf balls, polyurethane golf ball covers can be formulated to possess a softer “feel” like balata covered golf balls. However, golf ball covers made from polyurethane have not, to date, fully matched SURLYN® golf balls with respect to resilience or the rebound of a balata golf ball cover, which is a function of the initial velocity of a golf ball after impact with a golf club.
U.S. Pat. No. 3,989,568 discloses a three-component system employing either one or two polyurethane prepolymers and one or two polyol or fast-reacting diamine curing agents. The reactants chosen for the system must have different rates of reactions within two or more competing reactions.
U.S. Pat. No. 4,123,061 discloses a golf ball made from a polyurethane prepolymer of polyether and a curing agent, such as a trifunctional polyol, a tetrafunctional polyol, or a fast-reacting diamine curing agent.
U.S. Pat. No. 5,334,673 discloses a golf ball cover made from a composition of a thermosetting polyurethane prepolymer and a slow-reacting polyamine curing agent and/or a difunctional glycol. Resultant golf balls are found to have improved shear resistance and cut resistance compared to covers made from balata or SURLYN®. U.S. Pat. No. 5,692,974 discloses methods of using cationic ionomers in golf ball cover compositions. Additionally, the patent relates to golf balls having covers and cores incorporating urethane ionomers. Improved resiliency and initial velocity are achieved by the addition of an alkylating agent, such as t-butyl-chloride, which induces ionic interactions in the polyurethane to produce cationic type ionomers.
PCT Publication WO 98/37929 discloses a composition for golf ball covers that includes a blend of a diisocyanate/polyol prepolymer and a curing agent comprising a blend of a slow-reacting diamine and a fast-reacting diarnine. Improved “feel,” playability, and durability characteristics are exhibited.
U.S. Pat. No. 5,976,034 discloses a composition for a multi-layer, wound golf ball that have a solid center and a thermoplastic intermediate layer that form a dual layer core, rubber thread windings, and a thermoplastic cover. These golf balls are said to possess high initial velocity at low head speed region and excellent flight performance, without compromising shot “feel.”
U.S. Pat. No. 6,056,650 discloses a multi-piece golf ball having a solid core and a multi-layer cover having at least three layers, where the innermost cover layer and the outermost cover layer differ in hardness by not more than 3 Shore D units. These golf balls are said to possess increased flight distance when hit over a broad range of head speeds with any type of club, while maintaining feel, control, and durability.
Golf ball manufacturers are continually searching for new ways in which to provide wound golf balls that deliver the maximum performance for golfers. It would be advantageous to provide such a wound golf ball having improved playing characteristics.